1. Field of the Invention
The present invention relates to a DC/DC converter which reduces the breakdown voltage of elements.
2. Description of the Related Art
In general, power conversion systems are divided into converters and inverters. The converters serve to convert an AC input voltage into a DC voltage, and the inverters serve to convert a DC input voltage into an AC voltage.
Such power conversion systems are used to supply power to electric motors, lighting equipments, communication devices and so on. The power conversion systems control a voltage, supplied through a transformer, to a predetermined magnitude of voltage so as to drive the devices.
In particular, light emitting diodes (LED) are used for delivering a variety of signals in electronic products such as communication devices, TVs, monitors and so on. The LEDs used for delivering signals emit lights when an applied voltage is higher than a threshold voltage, and do not emit lights when an applied voltage is lower than the threshold voltage.
Recently, white LEDs have been developed, which have higher lighting efficiency than incandescent lamps. Accordingly, studies for substituting incandescent lamps and fluorescent lamps with LEDs are being conducted. Further, as for LEDs for lighting, high-brightness LEDs should be used, in which a large amount of current can flow and which can emit bright lights, unlike LEDs for signal delivery.
To obtain brightness required for such a lighting specification, a large number of LEDs should be arranged in series or in parallel to each other. In this case, when the LEDs are arranged in series, a plurality of driving voltages corresponding to the number of LEDs are needed. Accordingly, high driving voltages are required to obtain high brightness. As a result, the breakdown voltage of elements increases.
Hereinafter, a conventional DC/DC converter will be described with reference to FIGS. 1 to 3.
FIG. 1 is a block diagram of a conventional DC/DC converter. FIGS. 2 and 3 are block diagrams of modifications of the conventional DC/DC converter of FIG. 1.
As shown in FIG. 1, the conventional DC/DC converter includes a power factor correction (PFC) unit 10 which reduces harmonics of input voltages and a power loss, an insulation conversion unit 11 connected to the PFC unit 10, a constant current converting unit 12 which controls a driving voltage, output from the insulation conversion unit 11, to a predetermined magnitude, and then outputs the controlled driving voltage, and a load 13 which operates by receiving the driving voltage output through the constant current converting unit 12.
In this case, the conventional DC/DC converter can correct a power factor through the PFC unit 10. However, to satisfy safety standards, the insulation conversion unit 11 is required. The insulation conversion unit 11 converts a voltage, output from the PFC unit 10, into a DC voltage for driving the load, and then outputs the converted voltage. Further, the constant current converting unit 12 controls the driving voltage output through the insulation conversion unit 11 such that a constant current flows, thereby driving the load 13.
As shown in FIG. 2, the insulation conversion unit 11 and the constant current converting unit 12 may be combined as one insulation-constant current conversion unit 21. Alternatively, as shown in FIG. 3, the PFC unit 10 and the insulation conversion unit 11 may be combined as one power supply unit 30.
However, the conventional DC/DC converter has the following problems.
In the conventional DC/DC converter, the driving voltage output from the insulation conversion unit 11 is supplied to the constant current converting unit 12, and the constant current converting unit 12 controls the supplied driving voltage to deliver to the load 13. In this case, when the number of LEDs provided in the load 13 is increased, the magnitude of the driving voltage for driving the load 13 should be increased.
Accordingly, the insulation conversion unit 11 outputs a driving voltage with a large magnitude, and the constant current converting unit 12 having received the driving voltage should boost the received driving voltage to output. Therefore, the breakdown voltage of elements (not shown) composing the constant current converting unit 12 increases.
Further, when the breakdown voltage of the elements composing the constant current converting unit 12 increases, the size of the elements increases. Accordingly, the sizes of the constant current converting unit 12 and the DC/DC converter increase, and a manufacturing cost increases.